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A few days ago, my 97 Corolla had trouble starting. It cranks but doesn't start, maybe due to a problem with the carburetor. Figured I might discharge the battery, so I stopped my attempts at starting. Fast forward to this morning, I tried to start the car, but it had difficulty cranking, it was barely able to spin the pulley and was making a clicking noise. I measured and it was 10.5V.

I went to charge it with a 10 amp 12 v charger for like 8 hrs. I took a reading immediately after charging and it read 12.9V

I let the battery rest down, unconnected to the car, for 3 hours and when I checked, the voltage was back down to 10.5!

Is my battery busted? Should I try charging it for a longer time?

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Yes, this is a bad battery. One of the cells has most likely shorted. Each cell is a little above 2vdc. A fully charged battery will usually be ~13vdc. If you lose one cell, it will drop it down ~2vdc, which puts it right down in the arena of 10.5vdc. A direct short inside of a cell will allow electrons to pass through the short instead of raising the voltage, which is the reason you're still reading the 10.5vdc. Anyway, long story short: you need to replace your battery.

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  • 2
    To add, car batteries don't last forever and this is the most typical way for them to die. Decades ago the typical lifetime of a car battery would be two years, today you can expect 7 - 10 years from a good Exide or Varta in your '97 car, and possibly as little as two years again from the deep cycle type battery in a modern car with mileage-optimized charging and active stop-start system. – Pavel Jul 17 at 9:18
  • To determine the age of your battery, follow the steps outlined in this answer to read the date stamp. mechanics.stackexchange.com/a/70106/45516 – the_storyteller Jul 17 at 16:43
  • Yep, this is classic dead/shorted cell. If the rest of the cells are good you can probably charge it up to 12.5 V by severely overcharging them (most chargers will happily do this), but the voltage will slowly drop back down to around 10.5 or so after being removed from the charger. – R.. GitHub STOP HELPING ICE Jul 17 at 21:32

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